diag: Replace bit mask with array to check reg_dirty flag

Usage of bit mask for reg_dirty flag can result in a race
condition while handling multiple peripheral SSR. Replace
bit mask with array to make flag per peripheral to prevent
the race condition.

Change-Id: Id2662903c55eac3963b5ad34daaf4c2c2fdc24ed
Signed-off-by: Manoj Prabhu B <bmanoj@codeaurora.org>